The invention relates to a device and method for detecting the axial play of a gearbox shaft that meshes with a gearbox output, particularly a worm shaft of a gear motor actuator that meshes with a worm gear. Such actuators with a commutator motor and an adjoining worm gear are provided in particular for motor-driven closing systems, e.g. windows or sun roofs in motor vehicles.
Actuators of the aforementioned type, particularly in mass-produced units comprising a motor enclosure and a gear case with a continuous motor/gearbox shaft, exhibit undesirable tolerance-related axial play. This can cause end stop noises of the motor/gearbox shaft at the axial end stops on both sides as the direction of rotation is reversed.
To limit impermissible axial play, it is known, for instance, from EP 0 133 527 B2 to provide a spacer disk, which has a disk thickness that is based on a prior comparison between the actual, measured axial play and the desired axial play. This spacer disk is the contact part for at least one axial end face of the gearbox shaft, which merges into the motor shaft of a motor enclosure of a commutator motor that is flanged to the gear case receiving the gearbox shaft.
An object of the present invention is to detect, with little measurement complexity, the axial play of a gearbox shaft. It is another object to check the accuracy of an adjustment in cases where the gear parts or the motor drive parts have already been mounted in the gear case or the motor enclosure and their axial play has already been adjusted.
These and other objects are attained by a device for detecting the axial play of a gearbox shaft that meshes with a gearbox output, which device includes: means for rotationally driving the gearbox shaft between axial end stops of the gearbox shaft that limit axial play of the gearbox shaft; means for blocking the gearbox output while the gearbox shaft is driven; and means for determining a translational travel of the rotationally driven gearbox shaft between the axial end stops. The objects are also achieved by a method for detecting the axial play of a gearbox shaft that meshes with a gearbox output, the method including: rotationally driving the gearbox shaft between axial end stops of the gearbox shaft that limit the axial play of the gearbox shaft; blocking movement of the gearbox output during said rotational driving of the gearbox shaft; and determining the translational travel of the rotationally driven gearbox shaft. Advantageous embodiments of the invention are the subject of the dependent claims.
Blocking, e.g. locking, the gearbox output when the gear parts or motor parts have already been mounted and the gearbox shaft is already meshing with the gearbox output causes the motor drive to displace the gearbox shaft in a translational movement while it is secured relative to the gearbox output. As a result the actual axial play can be measured and the necessary adjustment determined, or it can be checked to ensure that the adjustment has already been made. For instance, if a spacer disk failed to be inserted due to an error or, if it was inserted, was lost again during the further assembly process, particularly during greasing, this defect can be detected.
The translational travel representing the corresponding axial play can be particularly easily determined by evaluating, in particular counting, the periodicity associated with the segment interruption of the commutator motor, i.e. the pulses of the driving commutator motor current or motor voltage characteristic, which has a corresponding ripple.
Determining the position of a part that is operationally displaced by a worm gear/commutator motor drive unit and is moved translationally or rotationally via the worm shaft and the worm gear meshing therewith by analyzing the commutation-dependent ripple of the motor current is known per se, for instance, from DE 41 38 194 A1.